In a ceramic utensil, such as pottery, china ware or porcelain, glassware or enamelware, gold or silver colored beautiful decoration is sometimes applied to its surface for imparting graceful or gorgeous impression. The conventional surface-decorated utensil is produced by coating a liquid gold (metal) containing an organic compound of noble metals, typified by gold resin balsam sulfide, on the surface of the utensil, by brushing or spraying or using a transfer paper etc., and subsequently firing the coated utensil. However, if the surface-decorated utensil, thus produced, is heated in, for example, an electronic range, sparks are generated on the surface of the decorative members of noble metal by the high-frequency electro-magnetic waves emanated by the electronic range thus producing cracks in the decorative members or peeling off of the decorative members. This is ascribable to the fact that the noble metal compounds making up the decorative members of noble metal is electrically conductive. For this reason, researches are recently under progress into the electrically non-conductive noble metal decorations insusceptible to damages when used in an electronic range.
For example, in JP Patents Kokal JP-A-55-51776 and JP-A-55-56079, a frit not containing or containing only a small amount of lead is added in a gold-colored or golden ingredient(s). it is stated in these Kokai publications that particles of noble metal are enclosed in the frit mixed therein and vitrified by melting of the frit caused by firing thus assuring excellent wear resistance and resistance against chemicals as well as excellent withstand voltage characteristics.
In JP Patents Kokoku JP-B-2-36558 and JP-B-5-13113 are disclosed liquid-gold or paste-gold for overglaze decoration comprised of a mixture of organic compounds of bismuth, indium and silicon. It is stated in these Patents that the noble metal decoration formed of the noble metal for overglaze decoration, that is a gold alloy, becomes electrically non-conductive by the presence of the above ingredients.
In JP Patent Kokai JP-A-6-48779, barium is added in addition to the ingredients that make the gold alloy electrically non-conductive for improving coloration in gold or silver color.
The conventional ceramic utensils, such as pottery, china ware or porcelain, glassware or enamelware, on which are applied gold or silver colored decorative members of noble metal usable on an electronic range, are made electrically insulating by adding insulating organic components in the form of organic compounds or frit into the noble metal for overglaze decoration, so that the utensil is not subjected to sparking when used in an electronic range.
In JP Patent Kokoku JP-B-3-3481 (or USA-4,713,512), there is described a tableware having a decorative member by net elements having spacings between the elements of at least 0.2 mm and a maximum size of 5 mm for withstanding microwaves.